In the field of manufacturing electronic devices, for example, semiconductor devices, organic substances and the like contained in the atmosphere of the manufacturing environment, for example, clean rooms, affect device performance and fabrication yield. These organic substances and the like are referred to herein as target substances. Consequently, it is desired to detect these target substances in the atmosphere.
In order to detect, by a simple method, target substances in the atmosphere, quartz crystal microbalance (QCM) sensors and the like using a quartz oscillator are used. QCM sensors utilize a phenomenon that the oscillation frequency of the quartz oscillator varies with a change in weight of the oscillator. In QCM sensors, when substances in the atmosphere adsorb to the surface of the oscillator, the presence of the substances is detected by a change in oscillation frequency of the quartz oscillator.
QCM sensors are used for environmental control in manufacturing plants and atmospheric control at various places. As substance sensors, in addition to QCM sensors using a quartz oscillator, sensors using a surface acoustic wave (SAW) element are also known.
For example, Japanese Unexamined Patent Application Publication No. 2002-48797 discloses a monitoring device and a monitoring method therefor in which an antibody that will bond to a specific substance to be measured is attached to the surface of an oscillator, and by measuring the change in output frequency of the oscillator with time, the change in mass of the substance bonded to the antibody is detected.
In the case where a quartz oscillator, which is used as a piezoelectric element, is provided with an antibody that is to be specifically bonded to a chemical substance (antigen) to be measured, and is oscillated by an oscillation circuit, the quartz oscillator oscillates with a given frequency in proportion to the amount of adsorption (mass) of the antibody. In this case, if the antibody reacts with the antigen, the mass of the quartz oscillator changes because of the reaction product. The change in mass is related to the change in frequency (number of oscillations) of the quartz oscillator in accordance with the equation: Δf=kf02 (Δw/A), where f0 is the initial frequency of the quartz oscillator, Δf is the change in frequency, Δw is the change in mass, A is the area of antigen deposited on the quartz oscillator, and k is the constant. For example, when a quartz oscillator with an initial frequency of 9 MHz is used, a change in mass of the conductive thin film of 0.5 ng/cm2 due to an antigen-antibody reaction can be measured with a sensitivity of 1 Hz.
For example, Japanese Unexamined Patent Application Publication No. 2009-98084 discloses an atmosphere analyzer which includes a counter electrode disposed so as to face a sensor electrode, in which a voltage is applied between the sensor electrode and the counter electrode to accelerate ions, and which includes an ultraviolet light source for applying ultraviolet light to the space between the sensor electrode and the counter electrode. When a target substance in the space is ionized by ultraviolet light, ions are driven by the electric field and adsorb to the sensor electrode. When irradiation with ultraviolet light is stopped, generation of ions is stopped. The sensitivity to the target substance can be improved by extracting the difference in signal between during irradiation with ultraviolet light and during non-irradiation with ultraviolet light.